I love Gentoo but I need something super-small I can run entirely from within a ramdisk on the 256MB Beaglebone. Can anyone recommend a super-small distro with good ARM support? I'm trying Tiny Core now but ARM support is new and I have yet to make it work 100%.

256 isn't too small. I think Gentoo runs fine for my needs. Gentoo is particular good because on many of these platforms optimization and compiler flags have a drastic impact on performance and its best to compile everything from source.